1. Field of the Invention
The present invention relates generally to a wireless sensor network and more particularly to a power saving method of sensor nodes of the wireless sensor network.
2. Description of the Related Art
Mainly due to the recent progress in wireless communications, Micro-Electro-Mechanical-Systems (MEMS) and microprocessor technology, the practical deployment of wireless sensor networks will soon become a reality. Such a network is envisioned as consisting of a large number of energy constrained devices, each of which is equipped with a radio transceiver, a small microprocessor and a number of sensing devices, and usually powered by a battery. These self-configurable nodes form a distributed network where the sensing information (generated by the scattered sensor nodes) is delivered to one or more sensing data collectors.
Because it is infeasible to replenish or recharge the battery of the sensor nodes, their operation is highly constrained by power so that the energy consumption of the nodes is the major operational constraint or concern. To relieve this constraint, many algorithms have been proposed for the lifetime of network itself to be extended.
Among the extensive list of studies on the energy efficiency, a widely used solution to reduce energy consumption is to put nodes to sleep or turn their radio off while they do not contribute to data delivery. This choice stems from the fact that energy consumption in idle mode is comparable to that in receiving mode and that the duration in idle mode makes up a significant fraction of the node's operational time.
Most notable among the algorithms proposed are the Basic Energy-Conserving Algorithm (BECA), the Adaptive Fidelity Energy-Conserving Algorithm (AFECA), and the Geographical Adaptive Fidelity (GAF). In BECA, the duty cycle (the ratio of idle time to the total operating time) is fixed, while AFECA adaptively decides the sleep period based on the number of neighbor nodes and GAF does this based on the redundant neighbors with the help of the location knowledge from Global Positioning System (GPS).
BECA determines the sojourn times of the nodes such that a node remaining in sleep/idle state can not receive even when there are traffic from other nodes, resulting in deterioration of the network performance.
AFECA adaptively determines the sojourn times depending on the number of adjacent nodes. In order to determine the sojourn times, it is required for the nodes to overhear traffic between the adjacent nodes even when there is no or a little adjacent node(s), resulting in unnecessary power consumption.
In GAF routing protocol, the locations of redundant nodes are discovered with the help of GPS and the sojourn times are determined on the basis of the number of the redundant nodes. However, the GAF is not applicable for sensor networks because of the expensive GPS utilization and much power consumption.